KR102129772B1 - Analog and digital dimming control for led driver - Google Patents

Analog and digital dimming control for led driver Download PDF

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Publication number
KR102129772B1
KR102129772B1 KR1020167025369A KR20167025369A KR102129772B1 KR 102129772 B1 KR102129772 B1 KR 102129772B1 KR 1020167025369 A KR1020167025369 A KR 1020167025369A KR 20167025369 A KR20167025369 A KR 20167025369A KR 102129772 B1 KR102129772 B1 KR 102129772B1
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South Korea
Prior art keywords
signal
input
analog
digital
dimming
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KR1020167025369A
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Korean (ko)
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KR20170124948A (en
Inventor
아드리안 왕
치엔-젠 수
웰턴 시
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다이오드 인코포레이티드
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Priority to US201562126440P priority Critical
Priority to US62/126,440 priority
Priority to US15/049,590 priority
Priority to US15/049,590 priority patent/US10178727B2/en
Application filed by 다이오드 인코포레이티드 filed Critical 다이오드 인코포레이티드
Priority to PCT/US2016/019463 priority patent/WO2016138204A1/en
Publication of KR20170124948A publication Critical patent/KR20170124948A/en
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    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B45/00Circuit arrangements for operating light emitting diodes [LED]
    • H05B45/10Controlling the intensity of the light
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B45/00Circuit arrangements for operating light emitting diodes [LED]
    • H05B45/30Driver circuits
    • H05B45/395Linear regulators
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05BELECTRIC HEATING; ELECTRIC LIGHTING NOT OTHERWISE PROVIDED FOR
    • H05B45/00Circuit arrangements for operating light emitting diodes [LED]
    • H05B45/40Details of LED load circuits
    • H05B45/44Details of LED load circuits with an active control inside an LED matrix

Abstract

The control circuit includes an input terminal that receives an input signal that can be a digital input signal or an analog input signal, and the control circuit is configured to provide a digital control signal in response to the input signal. The control circuit determines whether the input signal is a digital signal or an analog signal, and provides a mode detection circuit providing a mode signal, a multiplexer circuit configured to select a digital reference signal or an analog reference signal in response to the mode signal, and a PWM control signal To this end, a comparator circuit configured to compare the input signal with a reference signal selected by the multiplexer may be included.

Description

Analog and digital dimming control for LED driver{ANALOG AND DIGITAL DIMMING CONTROL FOR LED DRIVER}

This application claims priority to U.S. Provisional Application No. 62/126,440, filed on February 27, 2015, the contents of which are incorporated herein by reference in their entirety.

Light-emitting diodes (LEDs) offer many advantages over conventional lighting devices, such as long life, high efficiency and non-toxic materials. With the development of electronic technology, light emitting diodes are being applied to a wider field. For example, in consumer applications, LED lights can replace conventional white light incandescent or fluorescent bulbs. In addition, more electronic devices are adopting LCDs as displays, and LEDs are becoming more and more popular as backlight sources.

LEDs are usually regulated by controlling their current. Typically, LEDs are operated with a constant average current, and power electronic components are used to create a circuit that converts the AC voltage to a regulated LED constant average current to achieve the desired brightness. Dimming the brightness of the LED lamp can provide additional energy savings, improve flexibility, and improve the efficiency and life of the light source. The dimming of the LED string can be controlled by an analog dimming signal or a digital dimming signal. In analog dimming, the LED current varies with the magnitude of the dimming signal, but the LED is always on. In digital pulse width modulation (PWM) dimming, the LED on/off time varies, and the LED brightness is controlled by the duty cycle of the PWM dimming signal.

It is desirable that the LED driver can be operated by both analog and digital dimming control signals. One of the conventional approaches is to use two separate pins that accept analog and digital dimming signals. In some cases, two different control paths are used. The conventional approach uses a single input DIM pin to accept analog or digital dimming control signals. The control circuit determines whether the input signal is analog or digital. In the analog input dimming control mode, the LED current changes according to the magnitude of the analog dimming control signal. In the digital input dimming control mode, the LED current is determined by the duty cycle of the input signal. For both types of dimming control, output current regulation remains analog.

The inventors have recognized the limitations of conventional LED controllers that require two separate dimming signal pins to accept digital or analog dimming signals. The additional pin count increases the cost, especially for multi-channel LED drivers. In smart lighting applications, the controller often needs to control multiple channels. In these applications, high pin count not only increases component complexity, but also consumes a large chip size and circuit board area, making it undesirable for light bulb systems where space is limited.

In the conventional approach, A single DIM input pin is used to accept both analog and digital dimming control signals. However, the output LED current control remains analog. The disadvantage of this approach is that the controller chip tends to be large and consumes more power. In addition, analog dimming adjustment does not provide accurate dimming linearity at low current levels, particularly desirable in LED lighting systems.

The present invention provides a system and circuit for an LED control circuit that requires only a single input pin to provide a digital control signal that adjusts the current flow to respond to an analog dimming signal or digital dimming signal and control its brightness within an LED string. Teach. Contrary to conventional approaches, for both analog or digital input dimming control signals, an internal pulse mode modulation (PWM) driving a linear regulator to control on/off of the current flow in order to change its brightness within the LED. Digital control signals are provided.

For example, the control circuit may include a mode detection circuit for determining whether the input signal is a digital signal or an analog signal, a multiplexer circuit for selecting a digital reference signal or an analog reference signal, and a reference signal for selecting an input signal to provide an internal PWM control signal. It may include a comparator circuit to compare with. The LED driver can also include a constant current regulator that receives the internal PWM control signal and regulates the on/off of the current in the LED.

The analog reference signal may be a sawtooth signal, and the digital reference signal may be a constant voltage. The constant current regulator may include an amplifier circuit that connects the output current to a reference constant current. The amplifier circuit has an enable node that receives the PWM control signal and enables or disables the amplifier in response to the PWM control signal.

The single pin design with internal digital dimming improves dimming linearity, especially at low current levels and reduces the cost of the control circuit and the entire LED driver system.

1 is a simplified schematic diagram showing a power supply driving a light-emitting-diode (LED) lamp embodying a particular aspect of the present invention.
2 is a simplified schematic diagram showing a linear regulator embodying a particular aspect of the invention.
3 is a simplified waveform diagram showing a method of distinguishing an analog signal from a digital signal describing a specific aspect of the present invention.
4 is a simplified waveform diagram showing a method of converting an analog signal to a PWM digital signal describing a specific aspect of the present invention.
5 is a simplified schematic diagram showing an analog/digital mode detection circuit that implements certain aspects of the present invention.
6 is a simplified schematic diagram showing a constant current regulator embodying a particular aspect of the invention.
7 is a simplified schematic diagram showing a multi-channel linear regulator embodying a particular aspect of the invention.
8 is a simplified schematic diagram showing a switch mode power supply (SMPS) implementing a particular aspect of the present invention.

Justice

The terms used in this disclosure generally have their ordinary meaning in the art within the context of the present invention. Some terms are discussed below to further provide guidance to practitioners regarding the description of the present invention. It will be understood that the same can be mentioned in more than one way. As a result, terms and synonyms may be used.

Linear regulators are electronic circuits used to maintain a stable voltage. The linear regulator can place the regulator in parallel with the load (shunt regulator) or the regulator between the source and the regulated load (series regulator). The regulator acts like a variable resistor, continuing to regulate the voltage divider network to maintain a constant output voltage. Conversely, switching regulators use active devices that are switched on and off to maintain the average value of the desired output.

Constant current regulator is a linear regulator that provides a constant output current.

The LED (light - emitting diode , LED ) is a 2-lead semiconductor light source. It is a pn junction diode that emits light when activated. When an appropriate voltage is applied to the lead, electrons can recombine with holes in the device, releasing energy in the form of photons.

The analog signal is a continuous signal with variable time characteristics. It differs from digital signals that contain a series of discrete values that can only take one of a limited number of values.

Pulse width modulation (pulse - width modulation , PWM) is a modulation technique used to encode a message into a pulse signal by changing the on/off time. In the power regulator, the average value of the voltage (and current) supplied to the load is controlled by turning the switch between the power supply and the load on and off at a high speed. The longer the on time compared to the off time of the switch, the higher the total power supplied to the load. The term duty cycle refers to the ratio of the "on" time to a "interval" of time or a given interval. The low duty cycle corresponds to low power, since most of the time the power is off. The duty cycle is expressed as a percentage, and 100% indicates that it is entirely on.

A multiplexer ( multixer , mux ) circuit is an electronic device that selects one from a plurality of input signals and delivers the selected input to the output. The 2n input multiplexer has n select lines, which are used to select which input line is sent to the output.

State machines are mathematical computational models used to design both computer programs and sequential logic circuits. Conceptually, it is an abstract machine that can be one of a limited number of states. The machine is in only one state at a time, and the state at any given time is called the current state. When initiated by a triggering event or condition, it can change from one state to another, which is said to be before. A specific state machine is defined by a list of states and triggering conditions for each transition.

A comparator circuit is an electronic device that compares two voltages or currents and outputs a digital signal indicating which is greater.

1 is a simplified schematic diagram showing a power supply driving a light-emitting-diode (LED) lamp embodying a particular aspect of the present invention. As shown in FIG. 1, the power supply 100 includes an AC-DC converter 110 connected to an AC input source Vac to provide a DC voltage source Vin. The power supply 100 also includes a linear regulator 120 having a power terminal Vcc connected to a DC voltage source to receive a DC power supply Vin. 1, the DC power supply Vin is also configured to provide power to the LED lamp 130 having a plurality of LED strings. In Figure 1, Vin is connected to the anode of the LED string. However, Vin can also be connected to the cathode of the LED string. Linear regulator 120 also includes one or more channels 121 that are configured to regulate the current flow in the LED string. The linear regulator 120 also includes an output terminal (LED1, ..., LED4, etc.) connected to the LED string of the LED lamp and an input terminal (DIM1, ..., DIM4, etc.) that receives dimming input signals for each channel ).

2 is a simplified schematic diagram showing a linear regulator embodying a particular aspect of the invention. The linear regulator 200 is an embodiment of a linear regulator that can be used in the power supply 100. As shown in Fig. 2, the linear regulator 200 has a power terminal Vcc for receiving a DC power supply, which can also be configured to supply power to the LED lamp. As shown in FIG. 1 above, the linear regulator 200 may have one or more channels that regulate current flow in one or more LED strings. 2, only one channel 201 is shown for illustrative purposes. Each channel includes an input terminal (eg, DIM1) that receives an input signal. The input signal may be a digital input signal or an analog input signal. In some cases, the input signal can be a dimming control signal. The linear regulator 200 also has an output terminal (e.g. LED1) that connects each channel to the LED string of the LED lamp. Each channel is configured to regulate the current flow in the LED string based on the input signal. Each channel may include a control circuit 210 and a constant current regulator 220. The controller circuit 210 is connected to the input terminal to receive the input signal and provides a PWM digital control signal. The constant current regulator 220 is configured to receive an PWM control signal and provide an output signal at an output terminal (eg, LED1) to adjust the LED string of the LED lamp in response to the PWM signal.

As shown in FIG. 2, the linear regulator 200 includes a control circuit 210 and a constant current regulator 220 for each channel. The control circuit 210 includes, for example, an input terminal that receives an input signal from the terminal DIM1. The input signal can be a digital input signal or an analog input signal, and the control circuit 210 is configured to provide a digital control signal in response to the input signal. 2 illustrates the dimming control implementation, the input signal from DIM1 is a dimming control signal, and the control circuit 210 is configured to provide a digital control signal PWM to control dimming of the LED string connected to terminal LED1. However, the input signal is not limited to the dimming signal, and the output signal is not limited to the PWM signal.

As shown in Fig. 2, the control circuit 210 determines whether the input signal is a digital signal or an analog signal, and in Fig. 2, outputs a mode signal 232, also indicated by A/D, to indicate analog or digital. It includes a mode detection circuit 230 configured to. The control circuit 210 also has a multiplexer circuit 240, which is a selection terminal 241 connected to the output of the mode detection circuit, a first input terminal 243 for receiving an analog reference signal from the triangular wave generation circuit 250, A second input terminal 245 for receiving a digital reference signal from the digital reference signal generation circuit 260, and an output terminal 247 configured to provide a selected reference signal that is a digital reference signal or an analog reference signal in response to a mode signal It includes. The control circuit 210 also includes a first input terminal 271 connected to the input signal DIMl, a second input terminal 272 connected to the selected reference signal 247, and an output terminal providing a digital control signal PWM It has a comparator circuit 270 comprising 274.

In FIG. 2, the dimming mode detection block 230 detects whether the input signal is an analog signal or a digital signal, and provides a dimming mode indicator signal or a mode signal 232 to indicate whether the input signal is an analog dimming mode or a digital PWM dimming mode. do. The multiplexer 240 receives the mode signal and selects an analog reference signal or a digital reference signal accordingly. When the input signal is a digital PWM dimming signal, the digital reference signal may be a constant voltage having an appropriate voltage value to distinguish between high and low levels of the digital PWM dimming signal. For example, the digital reference signal can be set to 1.5 V. When the input signal is an analog dimming signal, its magnitude represents the desired dimmed light intensity. In these cases, the analog reference signal can be a triangular or ramp waveform, which is compared to the input analog signal to produce a digital PWM signal whose duty cycle indicates the desired LED intensity. The selected reference signal 247 is connected to the input terminal 272 of the comparator 270 and compared with the input signal DMI1 of the input terminal 271 of the comparator 270. Comparator 270 provides a digital PWM signal 274 at its output. The constant current regulator 220 controls the brightness of the LED string based on the digital PWM signal 274. The operation of the circuit block is described in more detail below.

now The operation of the mode detection circuit 230 will be described with reference to FIGS. 3-5. The controller determines the dimming control mode at startup or whenever the requirement to determine the dimming mode is satisfied. 3 is a simplified waveform diagram showing a method of distinguishing an analog signal from a digital signal describing a specific aspect of the present invention. As shown in FIG. 3, the analog dimming signal 310 typically slowly increases or decreases within a specific voltage range or band, for example, 0.4 V to 1.5 V. Conversely, a digital signal, such as the PWM dimming signal 320 in FIG. 3, typically toggles up or down quickly between power supply rails, eg, between 0 V and 3.3 V. The determination of whether it is an analog or digital signal can be performed within a given time period, for example 10 msec. During this time period, if the dimming signal toggles outside the expected analog voltage range at least a few times, the dimming signal is determined as a digital PWM dimming control signal. In FIG. 3, the voltage range is set between the PWM logic high threshold voltage 330 (2.5 V) and the logic low threshold voltage 340 (0.3 V). If the signal crosses the low and high threshold voltages at least a few times (e.g., twice) during a preset time period, it is determined as a digital PWM dimming control signal. This decision is reflected in the mode signal 232 in FIG. 2. The mode determination can be performed at start-up after the power supply has reached the minimum operating range.

4 is a simplified waveform diagram showing a method of converting an analog signal to a PWM digital signal describing a specific aspect of the present invention. The present invention teaches that analog signals can be converted to digital PWM signals by comparing them with a reference triangular or ramp waveform. As shown in Fig. 4, the analog signal 410 is compared with the triangular or ramp waveform 420 of the broken line. The digital signal 430 is formed such that the digital signal 430 is at a high level when the analog signal 410 is on a triangular waveform. Conversely, when the analog signal 410 is below the triangular waveform, the digital signal 430 is low level. In this embodiment, the triangular wave has a peak level set at 1.5 V and a valley level set at 0.4 V to cover the size range of the analog signal. As shown in FIG. 4, the digital PWM signal 430 has the same period T as the triangular wave 420, which is the sum T=Ton+Toff of the on time Ton and the off time Toff in the period. For example, in FIG. 4, Ton1 and Toff1 are within the first cycle, and Ton6 and Toff6 are within the sixth cycle. The duty cycle of the digital PWM signal 430 is the ratio of the on time Ton to the period T. Therefore, the duty cycle of the digital PWM signal indicates the magnitude of the analog signal in the period. Here, the period or frequency of the triangular wave is selected to provide sufficient sampling of analog input signal changes. For example, the frequency of the triangular wave may be 2KHz to 5KHz.

5 is a simplified schematic diagram showing an analog/digital mode detection circuit that implements certain aspects of the present invention. The mode detection circuit 500 is an embodiment of a mode detection circuit that can be used as the mode detection circuit 230 in the regulator 200 shown in FIG. 2 to determine whether the input signal is a digital signal or an analog signal. As shown in FIG. 5, the mode detection circuit 500 includes an input terminal 501 for receiving an input signal, which may be an analog signal or a digital signal, for example, DIM. The mode detection circuit 500 also has an output terminal 502 that provides an output signal A/D indicating whether the input signal is analog or digital. The mode detection circuit 500 also has two comparators 510 and 520 with reference voltages REF1 and REF2, respectively. REF1 may be set to the lower limit of the analog signal, for example, 0.4 V, and REF2 may be set to the upper limit of the analog signal, for example, 1.5 V. In addition, the mode detection circuit 500 has a counter circuit 530, a timer circuit 540, and a logic circuit block 550 connected to the circuit described above and providing an output signal at the terminal 502.

The mode detection circuit 500 determines whether the input signal is a digital or analog signal according to the method illustrated above in connection with FIG. 3. In this embodiment, the mode detection circuit 500 is configured to determine the number of times the input signal exceeds the reference signal during a preset time period, and if the number of times exceeds, for example, twice, the mode detection circuit 500 inputs Determine that the signal is a digital signal. During a preset period of time, the input signal increases from below the first reference voltage to above the second reference voltage, drops from above the second reference voltage below the first reference voltage, and again from below the first reference voltage to above the second reference voltage Increasing and dropping from above the second reference voltage to below the first reference voltage, it is determined that the input signal is a digital signal. The first and second reference signals span the reference voltage band, and the mode detection circuit 500 counts the number of times the analog input signal passes through the reference voltage band.

The mode detection circuit 500 is only an example of a possible implementation. Other circuits can be used to implement the mode detection circuit. For example, the mode detection circuit can be implemented using state machine design or using logic circuit elements. As an embodiment, if it is determined that one of the channels has received a digital PWM dimming signal, it can be assumed that all channels operate in a digital PWM dimming mode. Alternatively, each channel can determine whether its respective input signal is analog or digital.

6 is a simplified schematic diagram showing a constant current regulator embodying a particular aspect of the invention. The constant current regulator 600 is an embodiment of a regulator that can be used as the constant current regulator 220 of FIG. 2. As shown in FIG. 6, the constant current regulator 600 has an input terminal 601 receiving a digital PWM signal and an output terminal 602 connecting to the LED string to control the current flow in the LED string. The constant current regulator 600 supplies a current I1 and includes a constant current source 603 connected in series with the first resistor 612 (R1) at the first node 614. An optional first NMOS transistor 610, with a gate connected to the source to function as a diode, can be connected between the current source 603 and the first node 614. The output terminal 602 of the constant current regulator 600 is connected in series with the second NMOS transistor 620 and the second resistor 622 (R2). The second NMOS transistor 620 and the second resistor 622 are connected at the second node 624. The constant current regulator 600 is also connected to a first input 631 connected to a first node 614 between a first NMOS transistor and a first resistor and a second node 624 between a second NMOS transistor and a second resistor. It has an operational amplifier 630 that includes a second input 632. The operational amplifier 630 also has an output 634 connected to a node 618 connecting the gates of the first and second transistors. The operational amplifier 630 also has an enable node 636 (EN) connected to the PWM control signal.

The operational amplifier 630 is part of a feedback loop that associates the output current I2 with the input current I1 under the control of the PWM signal at the activation node EN. When the operational amplifier is enabled by the high-state PWM signal, the voltage of the first node 614 is equal to the voltage of the second node 624, and the current I2 flowing in the second NMOS transistor 620 is It is proportional to the current I1 of the constant current source 610 by factor n-ratio of the resistance of the first resistor R1 to the resistance of the second resistor R2. In other words, R1 =n*R2 and I2=n*Il. When the PWM signal is low, the operational amplifier 630 is turned off and the second NMOS transistor 620 is also turned off, causing the current I2 to be zero. In this way, the current I2 provided to the LED string at the output terminal is controlled by the PWM control signal. The average current of I2 is proportional to the duty cycle of the PWM signal. Therefore, when the PWM signal is a dimming control signal, the brightness of the LED string is proportional to the duty cycle of the PWM dimming signal.

7 is a simplified schematic diagram showing a multi-channel linear regulator embodying a particular aspect of the invention. As shown in FIG. 7, the linear regulator 700 has four channels 710, 720, 730, and 740, and can be used as the regulator 120 in the LED driving system of FIG. The channel regulates the current flow to the output terminals (LED1, ..., LED4) connected to the LED string of each LED lamp. The channels also have input terminals (DIM1, ..., DIM4) for receiving dimming input signals, respectively. Each channel includes analog and digital dimming circuits similar to dimming control circuit 210 in FIG. 2. Each channel also has a constant current regulator similar to the constant current regulator 220 in FIG. 2. In this embodiment, each channel has a separate dimming control. However, a single dimming control circuit can be used to control more than one channel or all channels.

In the above embodiments, a constant current regulator at a single input pin is combined with a control circuit that receives an analog dimming signal or a digital PWM dimming signal to form a linear regulator for dimming control of one or more LED strings. Linear regulators offer the advantage of fast computation and can respond to narrow PWM control pulses. However, the present invention is not limited to the specific embodiments described above. The control circuit described above can be used with other types of power supplies. For example, the control circuit can be used with a fly-back, buck, or boost configuration of a switch mode power supply (SMPS). One embodiment is described below with reference to FIG. 8.

8 is a simplified schematic diagram showing a controller for a switch mode power supply (SMPS) comprising one or more dimming control pins for accepting analog or digital control signals on the same pin. As shown in FIG. 8, the controller 800 has one or more dimming control pins (DIMs) that receive analog or digital dimming control signals, and the current to the LED string connected to the output pins (CH1, CH2, CH3, CH4) And a dimming control circuit 850 for controlling the flow. The PWM dimming & analog dimming block 810 is similar to the dimming control circuit 210 in FIG. 2, and the current sink 820 is similar to the constant current regulator 220 in FIG. Also, although only one PWM dimming & analog dimming block 810 is shown, there may be multiple such circuit blocks allowing independent dimming control of each channel.

As shown in FIG. 8, the SMPS controller 800 is a conventional PWM control function block such as a logic block indicated by Logic, PWM comparator (PWM), error amplifier (EA), overcurrent protection comparator (OCP), RS flip-flop, etc. It may include. The controller 800 also has an oscillator (OSC) that provides a clock signal (CLK) and a sawtooth signal (SAW). As described above, the present invention can also be implemented with a variety of configurations of switch mode power supplies (SMPS), such as flyback, buck, or boost configurations. The controller 800 includes a drive amplifier DRIVE that provides a control signal OUT to control the power switch to regulate the current flow in the inductor as a part of the converter in the flyback configuration or in the inductor in the buck or boost configuration. The controller 800 can also include a circuit block (BANDGAP, EN) and a reference to provide a reference voltage. Controller 800 may also include standard pins in conventional controllers such as VIN, EN, VCC, GND, CS, and COMP.

Claims (20)

  1. An input terminal for receiving an input signal;
    A mode detection circuit connected to the input terminal receiving the input signal, and configured to determine whether the input signal is a digital signal or an analog signal and provide a mode signal indicating whether the input signal is a digital signal or an analog signal;
    A multiplexer circuit configured to select a digital reference signal or an analog reference signal according to the mode signal, wherein the multiplexer circuit comprises: an output of the mode detection circuit, a first input terminal receiving the analog reference signal, and the digital reference signal Has a selection terminal connected to the second input terminal -; And
    A comparator circuit configured to compare the input signal with the selected reference signal and provide a pulse width modulation (PWM) control signal having a duty cycle determined based on the comparison,
    Dimming control circuit .
  2. According to claim 1,
    The mode detection circuit,
    Track the input signal for a preset period of time;
    If the input signal crosses the low and high threshold voltages at least twice during the preset period of time, it is determined that the input signal is a digital dimming input signal;
    Otherwise, configured to determine that the input signal is an analog dimming input signal,
    Dimming control circuit .
  3. According to claim 2,
    The preset time period and the low and high threshold voltages are selected based on the characteristics of the analog dimming input signal,
    Dimming control circuit .
  4. According to claim 3,
    The low threshold voltage is 0.3 V, and the high threshold voltage is 2.5 V,
    Dimming control circuit .
  5. According to claim 1,
    The mode detection circuit comprises two comparators, one timer circuit, one counter, and one logic circuit,
    Dimming control circuit .
  6. According to claim 1,
    The mode detection circuit comprises a state machine,
    Dimming control circuit .
  7. According to claim 1,
    The analog reference signal is characterized in that the sawtooth wave waveform (sawtooth wave waveform),
    Dimming control circuit .
  8. According to claim 1,
    The digital reference signal is a constant voltage signal,
    Dimming control circuit .
  9. According to claim 1,
    Further comprising a constant current regulator for receiving the PWM control signal to control the current flow in the LED, the constant current regulator,
    An input terminal receiving the PWM control signal;
    A constant current source connected in series with the first NMOS transistor and the first resistor;
    An output terminal connected in series with the second NMOS transistor and the second resistor; And
    Including an amplifier,
    The amplifier,
    A first input connected to a first node between the first NMOS transistor and the first resistor;
    A second input connected to a second node between the second NMOS transistor and the second resistor;
    An output connected to the gate of the first NMOS transistor and the gate of the second NMOS transistor; And
    Having an enable node connected to the PWM control signal,
    Dimming control circuit .
  10. In a control circuit that controls the flow of current to a light-emitting diode (LED):
    A single input pin configured to receive an input signal that can be one of a digital input signal and an analog input signal; And
    A digital output signal controlling the current flow in the LED and a single output pin configured to provide a digital signal in response to the analog input signal,
    Control circuit.
  11. The method of claim 10,
    A mode detection circuit connected to the single input pin receiving the input signal, and configured to determine whether the input signal is a digital signal or an analog signal and provide a mode signal indicating whether the input signal is a digital signal or an analog signal;
    A multiplexer circuit configured to select one of a digital reference signal and an analog reference signal in response to the mode signal, wherein the multiplexer circuit comprises: an output of the mode detection circuit, a first input terminal receiving the analog reference signal, and the digital reference Has a selection terminal connected to a second input terminal receiving a signal -; And
    Further comprising a comparator circuit configured to compare the input signal with a selected reference signal to provide a PWM control signal having a duty cycle associated with the desired output,
    Control circuit.
  12. The method of claim 11,
    The analog reference signal is characterized in that the sawtooth waveform,
    Control circuit .
  13. The method of claim 11,
    The digital reference signal is a constant voltage signal,
    Control circuit .
  14. In the linear regulator for driving a plurality of LED (light emitting diode) string (string),
    A power terminal receiving a DC power supply, wherein the DC power supply is configured to also provide power to the LED string;
    A plurality of channels; And
    Constant current regulator
    Including,
    Each of the plurality of channels,
    An input terminal for receiving an input signal that is a digital dimming signal or an analog dimming signal;
    A mode detection circuit connected to the input terminal receiving the input signal, and configured to determine whether the input signal is a digital signal or an analog signal and provide a mode signal indicating whether the input signal is a digital signal or an analog signal;
    A multiplexer circuit configured to select one of a digital reference signal and an analog reference signal in response to the mode signal, wherein the multiplexer circuit comprises: an output of the mode detection circuit, a first input terminal receiving the analog reference signal, and the digital reference Has a selection terminal connected to a second input terminal receiving a signal -; And
    And a comparator circuit configured to compare the input signal with a selected reference signal to provide a PWM control signal having a duty cycle associated with a desired output,
    The constant current regulator
    And a linear regulator configured to receive the PWM control signal to control the current flow in the LED string.
  15. The method of claim 14,
    The input signal is a dimming signal,
    Linear regulator.
  16. The method of claim 14,
    The mode detection circuit,
    Track the input signal for a preset period of time,
    If the input signal crosses the low and high threshold voltages at least twice during the preset time period, it is determined that the input signal is a digital dimming input signal,
    Otherwise, configured to determine that the input signal is an analog dimming input signal,
    Linear regulator.
  17. The method of claim 16,
    The preset time period and the low and high threshold voltages are selected based on the characteristics of the analog dimming input signal,
    Linear regulator.
  18. The method of claim 14,
    The analog reference signal is characterized in that a sawtooth waveform, the digital reference signal is a constant voltage signal,
    Linear regulator.
  19. The method of claim 14,
    The constant current regulator,
    An input terminal receiving the PWM control signal;
    A constant current source connected in series with the first NMOS transistor and the first resistor;
    An output terminal connected in series with the second NMOS transistor and the second resistor; And
    Including an amplifier,
    The amplifier,
    A first input connected to a first node between the first NMOS transistor and the first resistor;
    A second input connected to a second node between the second NMOS transistor and the second resistor;
    An output connected to the gate of the first NMOS transistor and the gate of the second NMOS transistor; And
    Having an enable node connected to a PWM control signal that enables or disables the amplifier in response to the PWM control signal,
    Linear regulator.
  20. The method of claim 19,
    When the amplifier is activated by the PWM control signal, the voltage at the first node is equal to the voltage at the second node, and the current flowing in the second NMOS transistor is the current of the constant current source multiplied by the index n, N is the ratio of the resistance of the first resistor to the resistance of the second resistor,
    Linear regulator.
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